雾化气体和冷却速度对镍基合金粉末凝固特性的影响

Influence of atomizing gas and cooling rate on solidification characterization of nickel-based superalloy powders

摘要:

镍基合金粉通过氩气雾化和氮气雾化制得。利用扫描电镜及其借助EDS能谱仪研究了雾化粉末的凝固微观结构特性。基于牛顿冷却模型，计算了雾化融滴的冷却速度和飞行速度。计算结果表明，雾化介质和融滴尺寸对冷却速度有影响，冷却速度也影响粉末的微观结构。对于氩气雾化粉，发达的枝晶结构在较低的冷速下获得；在较高的冷却速度下，得到混合的微观结构（枝晶和包晶）。对于氮气雾化粉，较低的冷速下得到枝晶；在较高的冷速下得到包晶。通过理论计算，氩气雾化粉末的冷却速度是10000K/s到424000 K/s，氮气雾化粉的冷却速度是10000K/s到480000 K/s。随着融滴尺寸的减小，两种雾化粉末的冷却速度则逐渐增加。元素Cr, Co, W, Ni 和 Al主要集中于晶轴，然而Ti主要集中于枝晶区域。

Abstract:

Nickel-based superalloy powders have been produced by high pressure argon gas and nitrogen gas atomization, respectively. The microstructural characterization of nickel-based alloy powders has been performed with the help of a scanning electron microscope, equipped with an EDS microanalysis unit. Based on a Newtonian cooling model, the flight speed and the cooling rate of two kinds of alloy droplets are calculated. The results show that the droplet cooling rate, which depends on atomization medium and droplet size, has an effect on the solidification microstructure. For argon-gas atomized powders, the developed dendrite structure is predominant at a lower cooling rate and a mixed microstructure composed of dendrite structure and cellular structure is observed at a higher cooling rate. For nitrogen-gas atomized powders, the dendrite structure is predominant at a lower cooling rate and a full cellular structure can be observed at a higher cooling rate. According to calculation, the cooling rate of argon-gas atomized droplets is in a range from10000K/s to 424000 K/s , while the cooling rate of nitrogen-gas atomized droplets is from 10000K/sto 480000 K/s . The cooling rate increases with decreasing of droplets diameter. Two kinds of atomizing gases have a slightly influence on the cooling rate of droplets. The elements such as Cr, Co, W, Ni and Al are rich in the dendrite axis, while Ti element is rich in the inter-dendrite region.